Military networks with HAIPE encryption and commercial networks with IPSec encryption may have communications links at the encrypted core that exhibit high rates of packet losses or can only provide limited bandwidth for VoIP applications. As such, the performance of VoIP applications may fall below acceptable levels.
For tactical wireless ad-hoc IP based networks, links can have limited bandwidth and may be unreliable because they can suffer from intermediate periods of fading, causing large packet loss. As a result, the performance of VoIP communications running on these networks may become degraded. This raises the need and desire to boost the performance of these applications such that VoIP decoders see less packet loss than is actually introduced by the network. In addition, because there is a low payload to overhead ratio for each packet transmitted over the network, it would be desirable to provide robustness without increasing the number of packets entering the encrypted core network. Moreover, reducing the number of packets entering the core network, referred to herein as compression, is desirable, when possible, to overcome the limited bandwidth of the encrypted core links.
VoIP boosting and compression techniques for tactical networks need to consider the effects and constraints of HAIPE. In such wireless VoIP networks, packet losses may be caused by, for example, the movement of the transmitting or the receiving terminals, electromagnetic interference, changes in environmental conditions, and other such factors. In networks utilizing HAIPE, in which packet size is substantially increased as a result of the encryption, the decryption technique checks for bit error. If any error in the packet is discovered, HAIPE drops the entire packet. In such encryption systems, packets with any missing or corrupted data are intentionally dropped or discarded by the encryption protocol, resulting in significantly higher packet losses than would occur without encryption. As a result, this behavior causes a HAIPE-encrypted VoIP network to introduce more packet loss to the VoIP stream. Moreover, because packet size substantially increases as the result of encryption, and because core network wireless links may have limited bandwidth, reducing the number of packets entering the core network is a key in achieving substantial compression over HAIPE.
VoIP “boosting techniques” (for robustness and compression) for tactical networks must be able to deal with the effects and constraints that such encryption techniques and limited bandwidth of wireless links impose on packet transfer.
Various error cancellation methods and forward error correction (FEC) techniques have been used to decrease unrecoverable losses or corruption of the packets entering a wireless VoIP network as described in, for instance, U.S. Pat. No. 6,785,261 issued to Schuster, et al. on Aug. 31, 2004 entitled “Method and system for forward error correction with different frame sizes,” the contents of which are hereby incorporated by reference. Other correction methods include relying on interpolating a missing packet based on adjacent packets as described in, for instance, U.S. Pat. No. 6,981,193 issued to Park on Dec. 27, 2005 entitled “Internet telephone and method for recovering voice data lost therein,” the contents of which are hereby incorporated by reference.
Various VoIP compression techniques are available in the literature and commercial applications that rely on reducing the bits/second rate of the encoded voice, which reduces the payload size of VoIP packets (e.g., the G.729 codec versus the G.711 codec). Tactical networks have more unique characteristics that require a different type of boosting (i.e., robustness and compression). This invention does not preclude the use of Forward Error Correction (“FEC”) at the wireless links or the use of compressed VoIP codecs. This invention performs VoIP boosting at the IP layer and works on IP packets before encryption and after decryption.
However, despite the considerable effort in the art devoted to development of reliable wireless VoIP communications, further improvements would be desirable, especially considering the need for a compromise between robustness and compression over HAIPE encrypted networks.